Modeling of Composite Electrodes

In the models discussed above, the constituent phases have different values of conductivity, but the conductivities are of the same type, i.e. they are both ionic or both electronic therefore, no special conditions apply at the boundaries between the phases. Examples of systans where this situation holds are polyphase zirconia ceramics (oxide ion condnctors), discussed in Section 4.1.3, and PTCR materials (electronic conductors). 

There seems to be no alternative to the generation of stochastic composite structures and their solution by computer methods. In a series of papers, Sunde has treated the bulk resistivity and polarization resistance for the steady-state (Sunde [1996a, 1996b]) and the electrode impedance in the frequency domain (Sunde [1997,2000]). Although this work focused on nickel/zirconia anodes, the methodology is equally valid for other composite electrodes. The first step was to use the Monte Carlo 

The presence of a new feature may be qualitatively explained in terms of the three types of clusters mentioned above. At low frequency only clusters of type (i) and (ii) are active, while, at high frequency, the double layer capacitance reduces the magnitude of the contact impedance and type (iii) clusters progressively switch in , producing a second arc. The degree of overlap of the arcs depends on the volume fraction of the electrode phase, an effect for which Sunde provides a tentative explanation at low volume fractions, where the overall impedance is dominated by the electrolyte, type (iii) clusters have a significant effect and generate a well- 

A valuable property of such modeling experiments is that all currents and potentials are stored and available for further analysis. A possible way of visualizing the function of the composite electrode would be to sum the partial electfonic and ionic currents at varions depths within the composite electrode and plot them as a fnnc-tion of position. The partial cnrrents could be used to identify the region of maximum charge transfer in the composite. 

---